Effect of asymmetrical K⁺ gradient (200 versus 77 mM and 200 versus 19 mM) on Kir4.1/Kir5.1 I-V relationships. (A – C, F, and G) Inside-out current traces from Kir4.1/Kir5.1 channels obtained using solutions containing the indicated K⁺ concentration. Currents were induced by voltage protocols as described in the text. (D and H) Normalized I–V relationships for currents evoked under conditions displayed in A (red circles), B (black line), C (blue triangles), F (maroon squares), and G (green circles). Note: Three additional test pulses are shown in H (empty marron squares) to illustrate the persistence of the inward rectification. Current amplitudes were measured at the end of the test pulses and normalized to the respective maximum value at each condition. Current traces in B are those from Fig. 2, which are only shown for comparison purposes, as well as the respective I-V relationship (continuous line in D). The inset at the right of D refers to the amplification of the area delimited in the box. (E and I) Current ratios for those obtained at the more depolarized and hyperpolarized potentials under the K⁺ concentration shown in A (red bar), C (blue bar), F (maroon bar), and G (green bar) measuring currents at the end of the test pulses. The dashed line denotes the zero-current level. Data are presented as mean ± SEM. n = 5–6 for all assayed conditions. *, P = 0.048; ***, P = 0.0002.